1. Field of the Invention
The present invention generally relates to fluid injectors for delivering high pressure fluid in a controlled manner. More particularly, the invention relates to an improved fuel injection nozzle for supplying fuel to an internal combustion engine. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Related Art
Fuel injection nozzles for supplying fuel to internal combustion engines are well known in the art. Such injectors typically employ an injector body which is affixed to an internal combustion engine such that one end thereof extends into an engine cylinder. The injector body defines an interior cavity which is fluidly connected with a fuel supply and includes a needle valve which cooperates with the injector body to selectively permit fluid received from the fuel supply to pass through the interior cavity of the injector body and into the engine cylinder. Since most internal combustion engines employ a plurality of cylinders, it is common to employ one or more of such injectors with each engine cylinder. Recent developments have focused on supplying fuel to these multiple injectors from a common fuel supply rail.
One type of injector described above is shown in FIG. 1A, the injector being shown in the non-injection phase of the injection cycle. The common rail injector 10 of FIG. 1 employs a hydraulic force imbalance scheme wherein a power piston 12 disposed at one end of a needle valve 14 cooperates with other components to control the net system forces acting upon the needle valve 14. In the design shown, a control chamber 16 which lies adjacent one end of the power piston 12 contains a volume of high-pressure fuel during the non-injection phase of the injection cycle. The force of this high-pressure fuel acts downwardly on the power piston 12 to oppose the upward force of the high-pressure fuel acting on annular seal 17 to thereby urge an opposite end 20 of the needle valve 14 to sealingly engage an apertured nozzle 22 of an injector body 24. In this state, the fuel supplied to the injector 10 is not permitted to pass into the engine cylinder. However, the pressure within the control chamber 16 can be relieved by energizing a solenoid actuator 30 to move a valve 26 and open a spill path 28 from the control chamber 16 to low pressure return 27 thereby decreasing the pressure in the control chamber 16. When the pressure within the control chamber 16 drops to a predetermined level, based on the geometry of various injector components, the needle valve 14 moves upwardly to permit fuel to flow through the injector body 24 and into the engine cylinder. De-energizing the solenoid actuator 30 closes the fuel spill path 28. The pressure within the control chamber 16 then increases until it overcomes the upward force acting on the seal 17 and the needle valve 14 is again urged into its initial position. With the fuel injection cycle, thus, completed, it can be repeated as desired.
Fuel injectors of the type discussed above suffer from a number of deficiencies which tend to limit overall performance. First, such injectors suffer from the limitation that they can only control opening and closing of the injector nozzle like a switch. Aside from transient needle movement, such "switch-type" injectors only permit the needle valve to maintain fully-open or fully-closed positions. Thus, they are not capable of modulating the needle valve position between these two extremes.
An additional deficiency associated with such injectors is that the needle valves thereof exhibit significant non-ideal transient movement characteristics stemming from their utilization of spill valves which are subjected to the large forces of their hydraulic force imbalance systems. In particular, these designs typically utilize a "hold down" spring such as spring 21 of FIG. 1 which supplies approximately 30-40 pounds of force to urge the spill valve 26 into sealing engagement with the spill path 28 during the non-injection phase of the injection cycle. This relatively large force must be overcome by the solenoid actuator 30 before movement of the needle valve 14 can occur. This directly results in a number of disadvantages. First, a minimum threshold time period is required to create a sufficient magnetic force in the solenoid to initiate spill valve 26 movement and, hence, the injection phase of the injection cycle. Similarly, deenergization of the solenoid at the end of the injection phase requires an additional period to time. This presents a limitation on the rate at which multiple injections can occur during each injection cycle. Second, the rate at which the needle can be moved from one position to another is necessarily limited by the high spring force which must be overcome to cause needle movement. Third, once the spill valve reaches one of its two extreme positions, the problem of dissipating the significant kinetic energy contained therein inevitably results in one or more of overshoot, undershoot, bouncing (alternating overshoot and undershoot) or ballistic trajectory of the spill valve. Since this spill valve movement ultimately controls needle valve movement, all of the above defects result in corresponding defects in needle valve movement. In summary, fuel injectors described above are deficient in that actuator and needle valve movement imperfections yield less than ideal control of valve behavior.
These problems are further exacerbated in fuel injector designs employing a safety disconnect feature. Generally, such safety features attempt to control the various injection events of an injection cycle by separating the high-pressure fuel supply from the combustion chamber in the event of injector failure. Since the fuel supply is disconnected from the engine cylinder, hazardous conditions such as overfueling can be avoided in the event of nozzle fracture and/or other failure. Such designs exacerbate the above-described deficiencies because selectively disconnecting the injector from the supply rail places the additional requirements of high flow capacity and high response rates onto the already stringent performance characteristics demanded of such injectors.
Therefore, there remains a need in the art for an improved fuel injector which overcomes the aforementioned deficiencies of the prior art by utilizing a small hydraulic force imbalance scheme acting on the actuator to achieve desired variable position of the needle valve in place of the typical two position control.
Further, there remains a need in the art for an improved safety fuel injector which overcomes the aforementioned deficiencies of the prior art by providing an "off-cycle" disconnect feature which automatically disconnects the injector nozzle from the supply rail during the non-injection phase of each injection cycle.
Additionally, a need remains in the art for a fuel injector which is capable of modulating the needle valve position to thereby throttle the fuel passing from the fuel supply into the engine cylinder.